| Popis: |
A low-latency, accurate RFID counting scheme can be used as a fundamental building block to support more elaborated RFID query operations. RFID counting algorithms of such nature have been proposed recently by Kodialam et. al. [2], [3]. One distinct feature of these schemes is that they do not require the reader to explicitly identify individual tags and thus can help to preserve privacy of the RFID users. However, these schemes all assume a perfect communication channel between the reader and the tags which is not achievable in practice. Recent empirical measurement studies have found that the radio communication between an RFID reader and a set of seemingly “in-range” tags are still unreliable and non-deterministic due to ever-changing channel conditions. Worse still, given the stringent cost constraint, it is unlikely that standard channel estimation procedures can be applied for individual tags. In this paper, we propose two new algorithms which can provide good estimates of the size of an RFID tag-set over unreliable, lossy wireless channels while assuming minimal or no prior knowledge of channel parameters. These algorithms are scalable over a wide range of tag-set size using a small, fixed protocol frame-size, which is critical for low-cost RFID tags with typically sub-par synchronization or timing control. They are also adaptive in the sense that, they self-tune the algorithm parameters according to the tag-set size and channel characteristics. This set of features makes them applicable in a wide variety of situations where the reader is unaware of or has very limited knowledge of the channel conditions. We also demonstrate the efficacy of the proposed schemes via extensive simulation studies. |
